1. Field of the Invention
The invention is directed to an electric circuit for downshifting a work vehicle such as a loader by depressing the differential lock switch.
2. Description of the Prior Art
When operating a loader the operator typically drives the loader in second gear between bucket loading operations. This speeds up the cycle time because the vehicle moves faster when not in the pile. On a loader with Forward-Neutral-Reverse (F-N-R) controls and a four speed gear control selector (1-2-3-4) a typical loading cycle, beginning with the loader in second gear as it approaches the pile to load the bucket, would be as follows:
1. downshift 2F-1F (left hand) PA0 2. engage differential lock (left foot) PA0 3. load bucket (right hand) PA0 4. shift F-R (left hand) PA0 5. upshift 1R-2R (left hand) PA0 6. shift 2R-2F (left hand PA0 7. dump bucket (right hand) PA0 8. shift 2F-2R (left hand) PA0 9. shift 2R-2F (left hand) PA0 10. approach pile repeat to 1
During these operations the operator is also steering the vehicle. On differential lock equipped loaders, as indicated at step 2, the operator depresses a differential lock switch with his left foot to increase traction and crowd during the loading operation. The differential lock switch maybe located to the left of the brake pedal and may comprise an electrical switch that triggers a solenoid valve for hydraulically locking the differential. As the differential lock switch is a non-latching electrical switch, the operator must maintain pressure on the switch as long as differential lock is desired. An electrically operated differential lock system is disclosed in U.S. Pat. No. 4,570,509 assigned to one of the assignees of the present invention, and which is incorporated herein by reference. U.S. Pat. No. 3,675,508 discloses an electrically actuated power shift transmission.
With the advent of electric shift transmissions it has become possible to use an electric switch located on the control lever to downshift the loader during the loading operation. Such a system is disclosed in U.S. Pat. No. 4,610,178. PCT Application WO87/06287 discloses a wheel loader that is automatically downshifted in response to bucket and boom parameters.